function dS = HCWModel( ~ , S , n )

dS= zeros(6,1);

dS(1:3) = S(4:6);
%[km/s] Current relative velocity in HCW Coordinate

dS(4) = 3 * n^2 * S(1) + 2 * n * S(5);
%[km/s^2] Current Relative x acceleration in HCW Coordinate frame

dS(5) = -2 * n * S(4);
%[km/s^2] Current Relative y acceleration in HCW Coordinate frame

dS(6) = -n^2 * S(3);
%[km/s^2] Current Relative z acceleration in HCW Coordinate frame

end